Steven,

I remembered that George Kaye mentioned that he sells dust cover for PSR9000. See the following thread:
http://www.synthworld.com/ubbs/Forum37/HTML/000011.html

George Kaye's business phone number is 818-881-5566

Paul Ip
from Texas

The following is George's own words:

I have dust covers that fit these two products. The yamaha is clear plastic and will only fit the 740. it sells for $15.00.
The other one is a black stretch type cover that fits inside a bag when you are not using it and stretches out of the bag to go around the keyboard. It sells for $24.00. I have also carried a cover made by Levy's that is a heavier material and is made to fit a particular keyboard. It sells for $32.00.

George Kaye